Light naphtha stream conversion to higher octane mixtures is an important part of the oil refining process and has been accomplished by a number of different catalysts in the past including such combinations as mixtures of hydrogen fluoride and antimony pentafluoride and mixtures of fluorosulfonic acid and antimony pentafluoride. The latter mixtures are called "super acid" catalysts in the art. However, for octane upgrading, HF-SbF.sub.5 mixtures are of only moderate activity and selectivity while FSO.sub.3 H-SbF.sub.5 mixtures, although having substantially better activities, have a relatively short catalyst lifetime in that cracking and other adverse side reactions set in after a short time on stream.
An example of the use of hydrogen fluoride-antimony pentafluoride mixtures is set out in Canadian Patent No. 742,746 in which use of HSbF.sub.6 and its mixtures with hydrogen fluoride are taught and an example of the use of fluorosulfonic acid-antimony pentafluoride mixtures is set forth in U.S. Pat. No. 3,766,286.
Now it has been found that by combining a fluorosulfonic acid-antimony pentafluoride catalyst with a small amount of hydrogen fluoride a far more selective conversion catalyst having an activity about the same as fluorosulfonic acid based catalysts is produced which has enormously improved catalyst lifetime as the hydrogen fluoride acts as a suppressor of unwanted side reactions. Thus, the usual octane upgrading processes such as isomerization which occur when the catalyst of the instant invention is in contact with hydrocarbons under the appropriate temperature, pressure and concentration conditions are effected with a substantially higher efficiency than has been heretofore obtained and considerable economic savings are obtained by the lowered amount of cracking and longer catalyst lifetime.